A conventional navigation apparatus displays the current position of a vehicle which is determined by a vehicle position calculating unit on a digital map (simply referred to as a “map” from here on) displayed on a display unit while superimposing the current position on the map. Furthermore, the conventional navigation apparatus searches for a recommended route from the current position of the vehicle which is determined by the vehicle position calculating unit to a destination inputted via an input unit, and displays the recommended route on the map. The conventional navigation apparatus then carries out a route guidance about the recommended route on the basis of the shapes of road links read from a recording medium.
By the way, recent years have seen increase in the number of cars owned by individuals and occurrence of traffic congestions in various parts of roads. Especially, most of vehicles traveling along a highway or expressway (simply referred to as a “highway” from here on in this specification) which is extending to a big city and which is used for commuting or the like are occupied by only one person and this results in increase in traffic congestions. In order to solve this problem, there have been constructed highways where traffic is restricted by law according to the conditions of vehicles including the number of passengers and vehicle types.
For example, a car pool lane (Car Pool Lane) which is adopted by a road system mainly seen in big cities of North American is an example. A car pool lane is also called an HOV lane (High Occupancy Vehicle Lane), and is a lane along which, for example, only vehicles in each of which two or more persons are riding are granted to travel. For example, a lane which is also provided on a highway is known as a car pool lane. A road system which adopts such a car pool lane provides users with a preferential treatment that makes it possible to arrive at the destination in a shorter time as long as they travel along a car pool lane so as to prod users to share a vehicle with one or more persons, thereby reducing the traffic as a whole and therefore reducing traffic congestions.
As a technology relevant to such a car pool lane, patent reference 1 discloses a vehicle-mounted navigation apparatus which searches for a recommended route in consideration of the number of passengers. This vehicle-mounted navigation apparatus has a storage unit for storing map data including link data about each link which constructs a road on a map. As for a car pool link on which restrictions of prohibiting a vehicle which is not occupied by two or more persons from traveling are imposed, the vehicle-mounted navigation apparatus uses link data including information showing that such restrictions are imposed on the car pool link to search for a recommended route from the place of departure to the destination. Furthermore, when a car pool link is included in the constitution links which construct the recommended route, the vehicle-mounted navigation apparatus receives an input of the number of passengers, and searches for a recommended route from the place of departure to the destination by using the link data to exclude links along which the vehicle cannot travel because the received number of passengers does not meet a certain criterion.
Patent reference 2 discloses a route searching apparatus which can perform a search for a route in consideration of the conditions of a vehicle through an easy operation. This route searching apparatus is provided with a map data acquiring unit for acquiring map data defined by nodes and road links, a route searching unit for searching for a route to a destination before the conditions of the vehicle are set up, taking into consideration a road link corresponding to a particular road for which whether or not the vehicle can travel according to the conditions of the vehicle is determined, the road link being included in the map data acquired by the map data acquiring unit, and an output unit for outputting the route searched for by the route searching unit.    [Patent reference 1] JP, 2005-061988,A    [Patent reference 2] JP, 2005-083758,A
A conventional navigation apparatus which can select whether to use a car pool lane as a search condition before performing a route search is known. However, there is a case in which while driving along a highway, the user would like to switch to a “route using” car pool lanes or a “route not using” car pool lanes after recognizing the road state of the highway. The conventional navigation apparatus is required to, in such a case, promptly present a “route using” car pool lanes or a “route not using” car pool lanes for the user in response to the user's prompt or easy operation.
The present invention is made in order to meet the above-mentioned requirement, and it is therefore an object of the present invention to provide a navigation apparatus which can promptly present a route using car pool lanes or a route not using car pool lanes for a user in response to the user's prompt or easy operation.